1. How many confirmations do you personally consider sufficient?
2. Would you accept zero-confirmation Bitcoin payments?
It's better to wait until 2 confirmations have been received before you can confirm the payment. 0 confirmations is only so risky because you need at least 1 confirmation before the transaction is recorded.
3. Should exchanges use different confirmation requirements depending on transaction value?
Exchanges don't need to use a higher number of confirmations. 2 confirmations is sufficient for them because their internal systems can detect incoming transactions to their deposit addresses and record them internally. Only until the number of confirmations exceeds the number of confirmations can they complete the transaction and allow users to withdraw their funds. As far as I know, if the number of confirmations isn't sufficient, you can only use it internally on the exchange and not withdraw it.
4. Do you believe Lightning is a practical solution for everyday Bitcoin payments?
The Bitcoin Lightning network isn't yet a viable solution for daily payments, as it still has several weaknesses and isn't practical. I prefer using other methods or cash for daily payments.
